The angle of inclination measures approximately 140° to 150° at birth, and during childhood development it progresses toward 125°. In the case where the angle is more horizontal straight (approaching 160° to 180°) it is called coxa valga, which can contribute to lower extremity genu varus (bow-legged). A more acute angle of inclination (approaching 90°) is called coxa vara and contributes to lower extremity genu valgus (knock-knees) (Neumann, 2016). The variations in angles of inclination are seen in Figure 2. With THA, the patient’s natural angle of inclination must be carefully considered by the physician when planning the surgery in order to restore normal joint alignment and prevent leg length discrepancies. Figure 2: The Angle of Inclination
degree of torsion of the femur on itself from its proximal to distal elements. Anteversion of 10º to 15º is considered to be normal but it can become excessive, or conversely, a hip could be retroverted. The variations in femoral head to acetabulum are displayed in Figure 3. Figure 3: Femoral Torsion Relative to the Acetabulum
A. Normal Anteversion
B. Excessive Anteversion
A. Normal
B. Coxa Vara
C. Coxa Valga
Note . From Neumann, D. (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation (3rd ed., page 484). © Elsevier. Reprinted with permission. Another element of anatomical alignment that needs to be considered during the planning for a THA is the degree of anteversion of the femur relative to the acetabulum. This is the Muscles and ligaments Motion at the hip joint is controlled by multiple muscles that cross the joint. The ability of many of these muscles to function optimally can be affected by two factors for those who have undergone THA. First, preoperatively the muscles are affected as a result of the progression of the degeneration of the hip where atrophy and/or reduced flexibility have occurred. Second, the impact on the muscles can be as a result of the surgical procedure where muscles are retracted and/or transected in order for the surgical components to be inserted. Several key muscles controlling motion at the hip are more prone to reduced flexibility; those are the hip flexors, such as iliopsoas and rectus femoris (Wylde et al., 2014). The hip adductors can also be affected in advanced degeneration of the hip joint, becoming tight and limiting active range of hip abduction (Westby, Brittain, & Backman, 2014). Depending on the surgical procedure used in the THA, there are several muscles, such as the gluteus medius or the internal rotators, which can be detached from the femur during the procedure to allow for the placement of the components of the THA. During the surgical procedure these muscles, which have been detached, typically will then be reattached. The reattachment of these muscles does not guarantee that the muscle will resume its preoperative level of contraction. For this reason, focused rehabilitation to address the patient’s ability to regain the use of these muscles can be crucial to regaining the function of these muscles around the hip joint. Individual muscles affected with specific surgical procedures will be identified in the section relating to the specific surgical procedures. In addition to the detachment and reattachment of specific muscles during the surgical procedure, the atrophy of key muscles, such as the gluteus maximus and medius, which frequently occurs in cases of longstanding hip degeneration, needs to be considered. Frequently the pain and reduced motion that accompanies degeneration of the hip joint leads to altered motion patterns in compensation. This can reduce the normal timing of action of these muscles during gait and
C. Retroversion
Note . From Neumann, D. (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation (3rd ed., page 485). © Elsevier. Reprinted with permission.
functional transfers, such as going from sitting to standing (Okoro et al., 2013). The hip joint itself is strengthened by a tough, fibrous joint capsule and a number of thick, strong ligaments named for their origins and insertions. These ligaments include the iliofemoral ligament (Y ligament), pubofemoral ligament, ischiofemoral ligament, and the ligament of the femoral head, also known as the round ligament of the femur, or ligamentum teres femoris. The round ligament inserts at the small indentation in the middle of the fovea, which is otherwise covered in smooth articular cartilage for a relatively friction-free gliding surface. The locations of these ligaments are displayed in Figure 4. Figure 4: Ligamentous Structures Around the Hip Joint
Ischiofemoral ligament
Iliofemoral ligament Acetabulum labrum Lunate surface
Ligamentum teres (cut)
Iliofemoral ligament
Acetabular fossa
Ligamentum teres (cut)
Lesser trochanter
Transverse acetabular ligament
Note . From Neumann, D. (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation (3rd ed., page 487). © Elsevier. Reprinted with permission.
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Book Code: PTNY3622B
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